Our earlier cryo-electron microscopic studies provided detailed insights into the three-dimensional (3D) organization of icosahedral PDH complexes. Our studies established the basic architecture that enables substrate channeling in this complex. The critical role of PDH at a central branch point in cellular metabolism is reflected by the multiple layers of regulation, often combined in a highly cell-specific manner, that control the precise flux of carbon between pyruvate and acetyl-CoA in response to cellular bioenergetic and biosynthetic requirements. In both bacterial and eukaryotic cells, rapid modulation of PDH activity can be accomplished by small metabolites and ions interacting directly with the complex, while long-term regulation occurs by transcriptional control of one or more of the constituent enzymes. The binding of one or more isoforms of pyruvate dehydrogenase kinase also serves an important regulatory role. We thus aim to pursue structural approaches that define the interaction of these various effectors that bind and potentially modulate function of the PDH complex. In another extension of these studies, we intend to explore the intersection between metabolic enzymes and key proteins relevant to cancer. p53 is an attractive target in oncology because its tumor-suppressor activity can potentially be stimulated to eradicate cancer cells. Activation of the p53 protein protects the organism against the propagation of cells that carry damaged DNA with potentially oncogenic mutations. MDM2, a p53-specific E3 ubiquitin ligase, is the principal cellular antagonist of p53 and its interaction with MDM2 is conformation-based and is tightly regulated on multiple levels. We are therefore initiating efforts to study the structures of p53-MDM2 complexes in the presence and absence of inhibitors.